The equation of an ellipse $E$ is $\dfrac {(y+2)^{2}}{81}+\dfrac {(x-2)^{2}}{36} = 1$. What are its center $(h, k)$ and its major and minor radius?
Solution: The equation of an ellipse with center $(h, k)$ is $ \dfrac{(x - h)^2}{a^2} + \dfrac{(y - k)^2}{b^2} = 1$ We can rewrite the given equation as $\dfrac{(x - 2)^2}{36} + \dfrac{(y - (-2))^2}{81} = 1 $ Thus, the center $(h, k) = (2, -2)$ $81$ is bigger than $36$ so the major radius is $\sqrt{81} = 9$ and the minor radius is $\sqrt{36} = 6$.